EP0548760B1 - Plasma ion nitrided stainless steel plates and method for the manufacture thereof - Google Patents

Plasma ion nitrided stainless steel plates and method for the manufacture thereof Download PDF

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Publication number
EP0548760B1
EP0548760B1 EP92121346A EP92121346A EP0548760B1 EP 0548760 B1 EP0548760 B1 EP 0548760B1 EP 92121346 A EP92121346 A EP 92121346A EP 92121346 A EP92121346 A EP 92121346A EP 0548760 B1 EP0548760 B1 EP 0548760B1
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EP
European Patent Office
Prior art keywords
press plate
press
plate
temperature
plates
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Expired - Lifetime
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EP92121346A
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German (de)
English (en)
French (fr)
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EP0548760A1 (en
Inventor
Kenneth J. Laurence
Wolfgang Kieferle
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Formica Corp
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Formica Corp
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/24—Nitriding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B38/00—Ancillary operations in connection with laminating processes
    • B32B38/06—Embossing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B30—PRESSES
    • B30B—PRESSES IN GENERAL
    • B30B15/00—Details of, or accessories for, presses; Auxiliary measures in connection with pressing
    • B30B15/06—Platens or press rams
    • B30B15/062—Press plates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
    • B32B37/10—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the pressing technique, e.g. using action of vacuum or fluid pressure
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/36—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases using ionised gases, e.g. ionitriding
    • C23C8/38—Treatment of ferrous surfaces
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/80—After-treatment
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S76/00—Metal tools and implements, making
    • Y10S76/02—Case hardening

Definitions

  • the present invention relates to a method for producing a ferrous press plate for producing decorative laminate, said press plate comprising a planar surface substantially defining the surface finish of said decorative laminate.
  • the present invention relates to a ferrous based press plate for producing decorative laminate.
  • Press plates used to produce decorative laminates are somewhat unique in overall geometry. Manufactured from various grades of steel, particularly stainless steel, the press plate is a flat sheet of rectangular cross section and often has comparatively large longitudinal and transverse dimensions, for example, as large as sixteen and five feet , respectively. The press plates, while thus having large planar surface areas, are only about one eighth of an inch thick.
  • press plates In a polished condition, the press plates ideally take on the appearance of a mirror-like sheet due to an extremely uniform planar surface, or microfinish, where microscopic discontinuities are minimized. Indeed, in the case of polished press plates, press plate microfinish quality can be determined by viewing reflected images on its surface and scrutinizing the reflected images for optical discrepancies.
  • Textured press plates produced by mechanically shot peening or chemically etching their planar surface, or combinations thereof, are usually of much lower gloss than polished plates, such that instrumental gloss measurement rather than visual reflectivity is usually the primary method of characterizing their quality, although certain defects are also evident with visual inspection.
  • Instrumental gloss measurements in ISO or NEMA gloss units, are typically established by the manufacturer of the laminate based upon consumer expectations. The laminate gloss level in turn is directly related to the gloss of the press plates from which it is produced. The greater the gloss of the plate, the more apparent plate wear becomes.
  • Warpage generally takes two forms. The first is a regular bow occurring over the entire longitudinal or transverse dimension. At modest levels, this bow is tolerable so long as the press plate assumes a nearly perfect planar orientation under the pressure of the press, which is normally in the range of 1000 to 1600 psi (6.9 to 11.0 N/mm 2 ). The second type of warp manifests itself as localized distortions and buckling, with variations in the relative height of the press plate from a hypothetically perfect planar surface.
  • press plates are generally used in a sandwich configuration with two composites of laminate resin-impregnated papers placed therebetween, facing opposite directions. Multiple layers of interleaved laminate material and press plates, so-called “packs” or “books”, are then loaded into a press for thermal curing and pressure treatment consolidation. If excess warpage of the first type or any warpage of the second type exists in the press plate, as well as imperfections in the surface microfinish, significantly deleterious effects on the finished decorative laminate appearance will be apparent.
  • ferrous based alloys have been surface hardened by various treatments involving the deposition and diffusion of additional elements and compounds into the base material, notably nitrogen and carbon.
  • additional elements and compounds notably nitrogen and carbon.
  • the wide variety of industrially practiced methods used to case harden stainless steel parts are suspectable to size restrictions and high processing temperatures, often requiring subsequent oil or water quenching, which can result in unacceptable surface finishes and part warpage.
  • these alternatives are impractical for treating large, relatively thin press plates.
  • the present invention unexpectedly has found that a concept known as plasma ion nitriding overcomes deficiencies inherent in known press plate hardening means and for the first time enables the manufacture of press plates for use in the production of wear resistant laminates containing concentrations of large alumina grit.
  • Many applications of plasma ion nitriding techniques have been applied to significantly smaller articles or larger articles with relatively small surface to volume ratios where the final microfinish has not been a critical cosmetic aspect of the article, such as via the MPT GmbH Plasma-Triding® process with an automated control and arc discharge suppression system, which regulates the plasma input energy for better control of the quality of work treatment. None of these applications suggested that plasma ion nitriding would be a solution to the problems solved by the present invention.
  • Plasma ion nitriding is based on plasma discharge physics and operates by exposing a negatively charged metal work piece surface to positively charged nitrogen ions. Under vacuum in a sealed vessel, an electrical potential is applied to the system, wherein the vessel becomes the positively charged anode (electron receptor) and the work piece forms the negatively charged cathode (cation receptor). High voltage energy is used to strip electrons from nitrogen bearing gas molecules introduced into the vessel, forming a plasma, where the nitrogen ions are accelerated toward the work piece. The impact of the nitrogen ions on the surface of the work piece generates heat energy from the conversion of kinetic energy to potential energy.
  • iron atoms predominantly are sputtered off at the point of impact to combine with other nitrogen ions forming iron nitride ions above the work piece surface in the glow discharge "seam". These iron nitride ions then impact and deposit on the heated work piece surface and diffuse into the subsurface molecular boundaries, creating an exposed surface layer and a distinct subsurface structure offering many of the desired characteristics for press plates as noted above, such as high hardness without brittleness, an unmarred surface finish, and a determined case depth.
  • the method for producing ferrous press plate according to the present invention is claimed in claim 1.
  • the ferrous based press plate is claimed in claim 5.
  • the application of the plasma ion nitriding process to large work pieces having very exacting final microfinish requirements, as disclosed by the present invention, is an advance due to the complicated relationships between parameter settings and expected results. These relationships include the work piece geometry, material surface and subsurface structure and desired results, process temperatures, pressures, and duration of heat-up time, thermal loading, radiant and convective heat energy effects, cooling system requirements, and gas mixture composition.
  • testing and analysis was coordinated to determine the proper functional parameters, the inter-relationship of functional parameters, and the allowable variance within each functional parameter or group of functional parameters to produce the desirable product specifications.
  • a general geometry formula was identified which describes the press plate surface area to thickness ratios for which the required parameters will apply.
  • Figure 1 illustrates the overall configuration of the reaction vessel 10 and the stainless steel press plate fixture 100 as installed.
  • the reaction vessel 10 related to the present invention is that used by the MPT GmbH PLASMA-TRIDING® process employing THERMION® processing and control equipment.
  • the vessel 10 includes a cylindrical outer wall 12, a cylindrical inner wall 13, and a cylindrical heat deflection shield 14, all located concentrically within the outer wall 12.
  • a cylindrical outer wall 12, a cylindrical inner wall 13, and a cylindrical heat deflection shield 14, all located concentrically within the outer wall 12.
  • an annular cooling water chamber 16 Between the outer wall 12 and the inner wall 13 is an annular cooling water chamber 16, wherein cooling water 18 is passed through to assist in maintaining the critical processing temperatures, as will be discussed below.
  • the outer wall 12, the inner wall 13, and the heat deflection shield 14 share a viewing port 20 to allow for visual "glow checks" of the press plate during the nitriding process.
  • the inner wall 13 and the heat deflection shield 14 are preferably formed from stainless steel or an alloy to prevent extraneous metals from becoming disassociated and contaminating the gaseous mixture treating the press plate.
  • the vessel 10 is further provided with a water supply 22 to provide the annular cooling water chamber 16 with a continuous regular source of cooling water to avoid excessive temperatures in the vessel 10, which if unchecked can contribute to excessive press plate temperatures and subsequent objectionable press plate warpage.
  • the vessel 10 is further provided with a vacuum pump 24, a gas supply containing nitrogen 26, a high voltage source 28, and a controller unit 30.
  • the high voltage source 28 provides a positive charged DC supply to the vessel 10 structure and a negative charged DC supply to the hanging fixture-press plate assembly 100 contained within.
  • the controller unit 30 corresponds to the THERMION® control equipment used in the MPT GmbH PLASMA-TRIDING® process.
  • the fixture 100 as shown in Figure 1 is comprised of base members 102, support rods 104, cross member 106, and support arms 108.
  • the press plate 50 is suspended from the support arms 108 with clamps 110 and hanging rods 112.
  • the press plates 50 must be separated by a distance sufficient to avoid interaction of the glow discharge plasma boundary of one press plate with that of the adjacent press plates. Further, this distance must minimize heat transfer from one press plate to the adjacent press plate to thereby avoid thermally induced distortions. Initial testing indicates that this distance is preferably about 8 inches (20.3 centimeters) or more, although other press plate dimensions may require different spacing criteria.
  • the clamps 110 are simple clevis devices supported by hanging rods 112.
  • a notch 116 is sized to slidingly accept the thickness of the press plate 50, which is usually about one eighth of an inch (3.175 mm).
  • the clamp 110 is affixed to the press plate 50 by tightening fasteners 118.
  • the clamp 110 is then attached to the support arms 108 through the hanging rods 112.
  • the clamp 110 is tapered inwardly toward the notch 116 by cutting or milling the projecting corners 120 away (shown in phantom).
  • the amount of mass which can absorb heat from the press plate 50 is minimized, which has been found to be a critical aspect of the present invention. It is very important that the press plate 50 be exposed to as little temperature gradations as possible to avoid warping.
  • the press plate 50 can be suspended in the vessel without substantial thermal interaction with the fixture 100.
  • the preferred method of nitriding is according to the MPT GmbH PLASMA-TRIDING® process using THERMION® processing and control equipment. This process utilizes electronic control equipment with arc discharge suppression control to minimize plate defects. Special processing conditions must be used for the press plates according to the present invention and are addressed below.
  • the energy of the impact of the nitrogen ions if uncontrolled, often generates heat energy and work piece temperatures capable of destroying the utility of large work pieces, such as press plates. This damage is evidenced by the deleterious effects of objectionable warping, buckling, and blemishes to the microfinish including imperfections such as arc trails ("spider marks” and "pimples"), localized meltdown (“comet tails”), clamp mark "halos", and other damage to the work piece. Accordingly, the commercial use of plasma nitriding for the hardening of large work pieces with exceptionally high surface to volume ratios, such as press plates, has heretofore not been considered viable.
  • the processing of the press plates to be treated in accordance with this invention begins with a pre-nitriding two-step cleaning procedure to remove water soluble, oil soluble, and insoluble residues from the work piece. These can often be attributed to the cause of "arc trails". The failure to remove any such residue can result in especially intense arc discharges during the initial nitriding process, which can damage the microfinish of the press plate 50.
  • the residues on the surface of a press plate typically are present in minute quantities resulting from earlier processing of the plate 50.
  • Freshly refinished polished plates although appearing visually clean, will still have residual polishing or buffing compounds (commonly called rouges) deposited on their surface.
  • Rouges typically are composed of a very fine abrasive material such as alumina combined with a waxy material (solid at room temperature which melts when applied to a warm plate during processing) or the abrasive material is combined with fatty acid "greases" in a water based emulsion (liquid at room temperature).
  • the most widely used release agents are fatty acid based, including common tallow acid soap (stearate/palmitate mixtures), zinc stearate powder (applied directly to the plate) and a variety of commercially available products well known to those versed in the art.
  • the two-step cleaning procedure involves first thoroughly cleaning a plate with deionized water. After allowing it to dry, the plate is then thoroughly washed with a chlorinated hydrocarbon solvent, of which 1,1,1-trichloroethane is the preferred solvent. In this manner, both water soluble and oil soluble materials are dissolved and removed from the plate, as are remaining insoluble particles by means of the physical washing action.
  • a chlorinated hydrocarbon solvent of which 1,1,1-trichloroethane is the preferred solvent.
  • the press plate 50 is then mounted in the fixture 100, as described above.
  • the loading and fixturing of the press plates has a direct impact on the selection of process parameters.
  • the thermal loading of the press plates generates radiant and convective heat energy, which in turn necessitates the proper modulation of the press plate temperature.
  • the dissipation of this heat energy generated is controlled through the modulation of the input voltage, the flow rate of the cooling water chamber 16, and the spacing of the press plates 50 within the vessel 10.
  • thermocouple 52 located within the loaded vessel 10 is a primary factor in modulating the heat energy generated within the vessel 10.
  • the thermocouple 52 placement at the edge of a centrally located press plate mounted to the fixture 100 has been found to be an ideal location for this geometry. Because of plasma physics and because of the ion bombardment on all surfaces of an "edge” or a “corner", this edge or corner will have the tendency to heat-up faster than the center of the plate 50. Therefore, the temperature of the outside surface of the press plate 50 will increase somewhat more quickly than the center of the plate.
  • the thermocouple 52 at the edge thus offers better control over the heat-up rate and a more consistent temperature profile through the cross section of the plate 50. Other locations for the thermocouple were found to lead to erroneous temperature data, which tends to confound controller 30 input and can lead to distortion and an uneven case hardness.
  • the vessel 10 is then filled with a nitrogen-containing gas, such as gaseous ammonia, at a pressure of 0.04 to 0.12 psi (3 to 8 millibar) through nitrogen gas supply 26.
  • a nitrogen-containing gas such as gaseous ammonia
  • Other gaseous mixtures containing nitrogen atoms may also be advantageously employed.
  • a nitrogen and hydrogen mixture would be recommended, as the hydrogen promotes the formation of chromium nitride.
  • this gaseous mixture can be more easily controlled for purity and dryness.
  • excessive concentrations of hydrogen in the presence of a base material having low or no chromium content can contribute to hydrogen embrittlement.
  • the use of carbon-bearing gases, such as methane, in the gas mixture is not recommended due to the deleterious effects of carburization.
  • a voltage is then applied to the system through the high voltage source 28 and a glow discharge forms about the press plate as the process enters the sputtering phase.
  • Arc discharges generated within the glow discharge are directed toward any remaining residue and deposits on the work piece and serves as a final cleaning process. Any such residue or deposits are thus vaporized and removed from the work piece.
  • the work piece itself has only increased moderately in temperature to about 93°C (200°F).
  • This phase corresponding to Region I of Figure 4, continues until all deposits are removed and the arc discharges diminish.
  • the voltage is then steadily increased, as shown in Region II of Figure 4, to accelerate the ion bombardment and begin the temperature rise to temperatures optimum for the nitriding phase.
  • the human eye is used to conduct a "glow check” operation.
  • a "glow check” through the port 20 of the vessel 10 to observe the uniformity and color of the glow discharge is made.
  • the press plate 50 begins to glow about its outside surface, it is important to allow the center of the press plate 50 to reach the same temperature without a large and potentially damaging temperature disparity between the edge and center press plate 50 portions.
  • the press plate 50 should be inspected for "hot spots" during this period.
  • glow color is directly proportional to the surface temperature of the press plate, any variations in color would indicate a variation in temperature, which should be avoided.
  • the temperature can be controlled via voltage input and the water flow rate through the water chamber 16.
  • the voltage is increased, as shown in Region IV of Figure 4, to 100 percent of that required to obtain the maximum desired temperature, and the automatic processing system is allowed to control the remaining processing, depicted as Region V of Figure 4.
  • the controller 30 is also used, while the vessel 10 is kept under vacuum to avoid oxidation on the press plate 50. The water flow in the cooling chamber 16 should also be maintained.
  • the selection of a parameter "set” depends on the desired hardness and case depth of the work piece. This hardness is manifest in two portions of the work piece; the compound layer and the diffusion zone.
  • the compound layer is formed on the exposed surface and is comprised essentially of ferrous nitride compounds and, in the case of stainless steel, a percentage of chromium nitride compounds.
  • the diffusion zone found beneath the compound layer, is hardened to a slightly lesser degree due to the propagation of nitrogen ions and ferrous nitride ions into the grain boundaries to form a decreasing concentration of nitride compounds.
  • the compound layer and diffusion zone to be hardened, defining the hardened case depth is related to the material and the geometry of the press plate 50. Note that the voltage potential (and corresponding temperature) and processing time are inversely related; if the processing time of Region V is extended, the overall maximum temperature can be reduced.
  • the geometry formula developed in conjunction with the present invention examines the surface area to thickness ratio.
  • the relationship of surface area in square feet to plate thickness in inches should be 150 square feet/inch to 2800 square feet/inch (5.5 square meters/centimeter to 102.5 square meters/centimeter). These values correspond to press plates having nominal dimensions of 3 feet by 7 feet (0.9 meter by 2.1 meters) having a thickness of one quarter inch (0.64 centimeter) and press plates having nominal dimensions of 5 feet by 16 feet (1.5 meters by 4.9 meters) having a thickness of one sixteenth inch (0.16 centimeter), respectively. Combinations of length, width, and thickness within these numeric ratios should be within the indicated parameters of the instant invention.
  • the preferred compound layer depth is between 0.0001 and 0.0004 inch (.0025 and 0.0102 millimeter).
  • the overall preferred case depth, including the compound layer and diffusion zone, is between 0.001 and 0.004 inch (0.025 and 0.102 millimeter).
  • other compound layer and diffusion zone thicknesses can be obtained depending on the specific requirements of the end product.
  • the vessel 10 is vented and the press plate 50 is removed from the unsealed vessel 10 only after it reaches room temperature.
  • the press plate 50 can be removed when its temperature cools to about 200°F (100°C).
  • removing the press plate 50 prior to its reaching room temperature reduces the processing time by six hours for productivity purposes, it also creates some oxidation on the plate surface caused by room temperature air coming into contact with the warm press plate 50 when the vessel 10 is opened. This layer can be rubbed off as necessary. If the work piece is allowed to reach room temperature, i.e. , a significantly extended cool-down period opposed to the shorter 2 to 8 hour period noted above, it has been found that a shinier finish with less oxidation may be obtained.
  • the oxidation caused by the room temperature air entering the vessel 10 while the press plate 50 is above room temperature may be avoided by the introduction of nitrogen or an inert gas into the vessel without voltage input to accelerate the final phase of the cooling process.
  • the surface finish of the laminate manufactured by the press plate can also be used to determine the press plate surface finish quality.
  • NEMA 60 degree gloss measurements are commonly used to characterize laminate finishes. As the marketplace has become much more critical in recent years, haze-free high gloss surfaces are now demanded. As such, the scale shown in Table B is generally accepted in the industry. Laminate Gloss Finish Quality ⁇ 100 excellent 95-99 good-very good 90-94 marginal ⁇ 90 unacceptable
  • the laminate produced from the 3u grit as 5 percent by weight of liquid resin in trial runs using a chromed polished plate suggests that deterioration in the plate and laminate microfinish occurred from microscratching.
  • the nitrided press plate exposed to 1 percent by weight of liquid resin 6 micron grit was rebuffed after 234 cycles and shown to produce acceptable laminate quality for at least another 103 cycles.
  • the 9 percent by weight of liquid resin 30 micron grit offers only limited press plate durability compared to smaller grit concentrations and sizes, it nevertheless indicates that the use of such aggressive grit formulations is possible if relatively frequent plate refinishing is acceptable (about the same frequency as a "dark" quality conventional polished plate).
  • press plates are used with composites of laminate resin impregnated treated papers placed therebetween, facing opposite directions, as shown in Figure 5. Multiple layers of press plates 50, laminate material 200, separator sheets 201, and cushions 203 placed on carrier trays or "pans” 207 to form "packs" 202, which are then loaded into a press 204 between heating/cooling platens 205 for temperature and pressure treatment consolidation and curing.
  • the invention herein disclosed is not limited to high pressure decorative laminate, but can also be beneficially applied to low pressure decorative laminates, such as those containing a particleboard or medium density fiberboard substrate rather than a plurality, of phenolic resin impregnated cellulosic core sheets of the high pressure decorative laminate (surfaced with a print or solid color sheet and optionally, an overlay sheet).
  • low pressure laminates In contrast to the cure period of about 45 to 90 minutes at pressures ranging from 1000 to 1600 psi (6.9 to 11.0 N/mm 2 ) for pressing high pressure laminate, low pressure laminates have cycle times of about 1 minute at pressures of 200 to 300 psi (1.4 to 2.1 N/mm 2 ).
  • the use of aggressive grit formulations or other hard materials in the laminate at the rapid cycle rates used to produce low pressure laminates will quickly deteriorate the press plates of such applications. Therefore, the utility of the present invention should be applicable to a wide range of decorative laminate products.
  • 630 stainless steel is similar to 410 stainless steel, but has about half the carbon content (0.05-0.08% versus 0.15%) while maintaining equivalent hardness (42-45 HRc) by means of a special precipitation hardening process.
  • the lower carbon content is preferred for chemical etching of textured plates.
  • a trial with a full size (4 feet by 10 feet (1.22 by 3.05 meters)) textured plate according to the present invention increased the case hardness to 67-70 HRc from 42-45 HRc.
  • 304 stainless steel is an annealed "bulk unhardenable" austenitic stainless steel with high chromium content (18.0-20.0 versus 11.5-13.5) and nickel content (8.0-10.5 versus 0.75) compared to 410 stainless steel.
  • 304 stainless steel press plates including high gloss mirror finish plates, are sold commercially and used as press plates due to their lower cost, they are also very susceptible to scratching and other plate handling damage due to their softness.
  • 304 stainless steel is so soft that it bearly registers on the Rockwell C hardness scale (comparative hardness on the "softer" Brinell scale are 140 for the 304 alloy and 390 for the 410 alloy).

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  • Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Laminated Bodies (AREA)
  • Chemical Vapour Deposition (AREA)
  • Casting Or Compression Moulding Of Plastics Or The Like (AREA)
  • Ceramic Products (AREA)
EP92121346A 1991-12-19 1992-12-15 Plasma ion nitrided stainless steel plates and method for the manufacture thereof Expired - Lifetime EP0548760B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US07/810,244 US5244375A (en) 1991-12-19 1991-12-19 Plasma ion nitrided stainless steel press plates and applications for same
US810244 1991-12-19

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EP0548760A1 EP0548760A1 (en) 1993-06-30
EP0548760B1 true EP0548760B1 (en) 2000-02-23

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TW249248B (zh) 1995-06-11
EP0548760A1 (en) 1993-06-30
SE9203739D0 (sv) 1992-12-11
DE69230706T2 (de) 2000-08-10
ES2142311T3 (es) 2000-04-16
SE511732C2 (sv) 1999-11-15
MX9207359A (es) 1994-02-28
US5244375A (en) 1993-09-14
DE69230706D1 (de) 2000-03-30
SE9203739L (sv) 1993-06-20
JPH0734219A (ja) 1995-02-03
NZ245181A (en) 1995-12-21
CA2083317A1 (en) 1993-06-20
AU3001992A (en) 1993-06-24
CA2083317C (en) 2000-01-18
AU651780B2 (en) 1994-07-28
KR930013196A (ko) 1993-07-21
CN1083126A (zh) 1994-03-02
ATE189906T1 (de) 2000-03-15
US5306531A (en) 1994-04-26

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